Precision Measurement of the Weak Charge of the Proton

Abstract

The fields of particle and nuclear physics have undertaken extensive programs to search for evidence of physics beyond that explained by current theories. The observation of the Higgs boson at the Large Hadron Collider completed the set of particles predicted by the Standard Model (SM), currently the best description of fundamental particles and forces. However, the theory's limitations include a failure to predict fundamental parameters and the inability to account for dark matter/energy, gravity, and the matter-antimater asymmetry in the universe, among other phenomena. Given the lack of additional particles found so far through direct searches in the post-Higgs era, indirect searches utilizing precise measurements of well predicted SM observables allow highly targeted alternative tests for physics beyond the SM. Indirect searches have the potential to reach mass/energy scales beyond those directly accessible by today's high-energy accelerators. The value of the weak charge of the proton Q_W^p is an example of such an indirect search, as it sets the strength of the proton's interaction with particles via the well-predicted neutral electroweak force. Parity violation (invariance under spatial inversion (x,y,z) -> (-x,-y,-z)) is violated only in the weak interaction, thus providing a unique tool to isolate the weak interaction in order to measure the proton's weak charge. Here we report Q_W^p=0.0719+-0.0045, as extracted from our measured parity-violating (PV) polarized electron-proton scattering asymmetry, A_ep=-226.5+-9.3 ppb. Our value of Q_W^p is in excellent agreement with the SM, and sets multi-TeV-scale constraints on any semi-leptonic PV physics not described within the SM.

Direct link to Nature Version "https://rdcu.be/954U"

References in corpus (8)

• Measurement of Strange Quark Contributions to the Vector Form Factors of the Proton at Q**2=0.22 (GeV/c)**2
• Testing the Standard Model by precision measurement of the weak charges of quarks
• Realistic Transverse Images of the Proton Charge and Magnetic Densities
• Global Analysis of Nucleon Strange Form Factors at Low $Q^2$
• Parity-Violating Electron Scattering and the Electric and Magnetic Strange Form Factors of the Nucleon
• Precise determination of low-Q nucleon electromagnetic form factors and their impact on parity-violating e-p elastic scattering
• Analyzing power in elastic scattering of the electrons off a spin-0 target
• A novel comparison of Møller and Compton electron-beam polarimeters

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